In an electronic blood pressure meter for detecting blood pressure values from a finger, the finger is, first of all, placed in a finger cuff for applying pressure to the finger, and blood pressure values are then computed from the change in the amplitude of pulse wave obtained from the finger as the cuff pressure is gradually reduced, according to a certain algorithm applied to a series of pulse wave data. In such an electronic blood pressure meter, since the finger cuff has inflatable air chambers which are limited in capacity as compared to an arm cuff which is more commonly used for measuring blood pressure, the cuff is less resistant against excessive pressurization particularly when the air chambers are inflated without placing a finger in the cuff. Further, if an excessive pressure is applied to the pressure sensor due to absence of a finger in the cuff, the pressure sensor may be damaged. Therefore, it is highly desirable not to inflate the cuff until a finger is placed in the cuff.
Conventionally, a micro switch was typically used for detecting presence of a finger in a finger cuff, but the micro switch occupies such a large space that the size of the finger cuff becomes larger than desired. And, some difficulty arises in assuring the reliability of the operation of the micro switch. An alternative possibility is to place a photoelectric sensor for detecting presence of a finger in the cuff, but the need for special component parts increases the complexity of the sensor and the manufacturing cost.